That one piece is for initialization. I'm not sure about wireguard, but I've typically seen that abstractions of ethernet stacks like VPNs will either throw away packets to be sent before initialization is complete, or will structurally simply not allow anything to be queued at that point in the first place (so like if it's a user space implementation, use type safety somehow so you can't even call send_packet() until it's done with init). In those modes the fixed latency of init doesn't cause buffer bloat issues.